A well-known video imaging system is that used in television, wherein the lens of the TV camera focuses energy to be imaged onto a focal plane surface. At optical wave lengths, this surface may consist of a photosensitive surface on an appropriate supporting structure. At millimeter (mm) wave lengths, the lens is substantially larger and the energy sensing surface is formed by an array of antennas, each of which feeds a detector. If the distance from the lens to the focal plane, divided by the diameter of the lens equals one (f/D=1), the antennas would be spaced apart a distance equal to one wavelength (.lambda.). Such a focal plane array, used in combination with a mm-wavelength lens, can be considered to be a mm-wave TV camera.
Printed arrays of antennas integrated with detectors have been constructed in both open (dipole) and closed form. Dipoles are more susceptible to high power interference from low frequency radars than arrays of open ended waveguide antennas (which as described below are employed by the present invention), because of the high attenuation of energy below waveguide cut-off provided by open ended waveguide antennas. A mm wave vidicon involving detectors read by an electron beam has been previously suggested.